This invention pertains to a drive mechanism for applying torque uni-directionally to a drive wheel, and in particular, to such a mechanism having a pair of reciprocating force-interacting sheaves.
This invention was developed with reference to land-traveling human-powered vehicles, but may be used in other applications. The invention, as originally conceived, was intended to be used by handicapped persons who are able only to use the quadricipital muscle in the leg, and therefore, are able to extend the leg but are unable to retract it. Additionally, there are such handicapped persons who are able to extend one leg further than the other.
In response to this, as well as other perceived needs, various human-powered vehicles have been developed which are propelled by reciprocating leg motion. Typically, a downward force is applied alternately on a pair of pedals or lever arms in order to propel the vehicle. The pedals are usually connected by various means so that a downward force on one pedal causes the other pedal to rise. Such pedal interconnections are sometimes via a cable extending around pulleys. Constant tension on the cable is required to hold it in position. Alternatively, rigid members are sometimes used in order to assure cooperating reverse and forward motion between the pedals.
It is also desirable to have direct force coupling between a pair of reciprocatable lever arms. This is particularly true with reference to developments in the area of human-powered racing vehicles. Such vehicles typically require the ability to apply driving forces in both reciprocating directions of movement of a lever arm, such as a foot or hand lever, in order to maximize the power applied to the vehicle. Inventions presently known to applicant either provide force application in one direction of a reciprocating-motion device or require a full continuous rotation in a single direction.
It is therefore a general object of a device made in accordance with this invention to overcome some of the disadvantages of the known prior art.
In particular, it is an object to provide a reciprocating-motion device in which forces may be applied continuously.
It is a further object to provide such a device using flexible elements, such as cable, for providing direct force transfer from one force-applying member to another through both directions of reciprocating motion of that member.
Further objects of this invention are to provide a device in which the length of the reciprocating strokes are variable within the limits of operation of the device and to provide for varying the length of strokes between the two force-applying members.
Such objects may be achieved on a vehicle having a rotatable drive wheel which applies the necessary driving force for propelling the vehicle or other appropriate use. Such a vehicle has conventional free-wheeling hubs which may be rotated alternately or jointly in order to apply a rotational torque to the drive wheel when rotated in one direction and to apply no force to the wheel when rotated in the opposite direction. The invention includes a pair of sheaves rotatably mountable on a frame of the vehicle and two sets of adjacent pulleys. A pair of cables, each having one end attached to each sheave rim, extends around a separate set of pulleys in such a manner that the two cables apply, when in tension, opposing rotational forces on each sheave. A lever arm is attached to each sheave for applying reciprocating motion.
It can be seen that such a device provides continuous force application through manipulation of one lever arm or through alternate force application on each lever arm, as is appropriate in a given application. It can also be seen that any length of stroke may be used depending on the length of the arc travelable by each sheave.
Additionally, the radius and arc length of the two sheaves may be unequal in order to provide for less movement by one sheave compared to the other.
These and additional objects and advantages of the present invention will be more clearly understood from a consideration of the drawings and the following detailed description of the preferred embodiments.